1. Field of the Invention
The present invention relates to an IP (Internet Protocol) communications system and a method of allocating an IP address for the same. The present invention may, as an example, be applied to allocation of IP addresses in a VoIP (Voice over IP) telephone system.
2. Description of the Background Art
The VoIP signaling protocol is based on the master-slave type of architecture in which a master-slave relationship is established between devices making up a system in such a fashion that a gateway device for use in interconnecting terminal devices or different networks with each other is controlled by a gateway controller to thereby set up and control calls. More specifically, in the VoIP signaling protocol, such as Media Gateway Control Protocol (MGCP) or ITU-T (International Telecommunication Union Telecommunication Standardization Sector) Recommendations H.248.1 for TTC standard/Media Gateway Control (MEGACO), a media gateway (MG) acting as a gateway device is controlled by a media gateway controller (MGC) functioning as a gateway controller to establish or control calls under a master-slave relationship. The media gateway controller serves as a master and the media gateway as a slave.
For the Media Gateway Control Protocol, reference is made to IETF RFC3435, “Media Gateway Control Protocol (MGCP) Version 1.0”, F. Andreasen and B. Foster, January 2003.
In an IP communications system constructed on the basis of such a protocol, for example a VoIP telephone system, the media gateway controller manages at least information specifying each of the media gateways it supervises and controls and in addition information as to how to control the media gateways.
For example, when a subscriber has connected the media gateway to a network, turns the power supply on, and completes the initial setting of the media gateway to set up its usable state, the media gateway notifies a specific media gateway controller controlling the media gateway itself of the readiness for use of that media gateway. Upon notified, the media gateway controller recognizes that the media gateway which has been notified is one of the media gateways the media gateway controller is to control, and instructs the operating conditions under which the media gateway controller supervises for the media gateway in question. The media gateway then operates under the operating conditions instructed by the media gateway controller.
An illustrative operation will proceed as read below. For example, when the handset of a telephone subscriber set, connected to the media gateway in question, is off-hooked, the media gateway notifies the media gateway controller of that off-hook condition, and sends out a dial tone. The media gateway receives the digit signals being dialed, and transfers, upon termination of the dialing, the received digit signals to the media gateway controller to await instructions following thereto.
In VoIP, the destination of a message transmitted between a media gateway controller and a media gateway is defined by an IP address. That gives rise to a method which, when a media gateway controller controls a media gateway, the media gateway controller is advised of the IP address of the media gateway, as information specifying the media gateway, at the outset, and performs control accordingly. Specifically, the media gateway controller permanently allocates an IP address to a media gateway, when assigned to a subscriber, to thereby able to manage the relationship of correspondence between the media gateway and the IP address. Since in such a management method, the IP address, allocated to a media gateway, is not changed as long as the media gateway remains the same, the management of information on the media gateway, such as its IP address, may be facilitated.
On the other hand, since the IP addresses under the Internet Protocol version 4 (IPv4), regulated by RFC791, so far used extensively, is of a 32-bit length, there is raised a problem that, if IP addresses are to be permanently allocated to media gateways, the IP addresses fall into shortage in IP address resources. There is also raised a problem in case a business organization providing VoIP services, or VoIP service provider, does not keep IP addresses sufficient for permanently being allocated to the subscribers therefor. Moreover, a business organization allocating IP addresses may differ from a business organization providing VoIP services. In such a case, in order to allot permanent IP addresses to media gateways, it is necessary to circulate information on IP address allocation among those different business organizations. There is however raised a further problem that such information circulation is time-consuming or expensive.